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Control Circuit For Controlling Power Supplied To An Igniter Element And Igniter System - Patent 5957988

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FIELDOF THE INVENTIONThis invention relates to a control circuit for controlling power supplied to an igniter element and an igniter system.BACKGROUND OF THE INVENTIONIgniter devices are used commonly in applications such as airbag deployment and seat belt pretensioner activation in cars. The igniter device comprises an igniter element which converts electrical energy to heat. Typically, the igniter elementcomprises a hot wire bridge which is heated by a current of 1 Amp (A) or more. In, for example, airbag applications, the heat generated in the igniter element ignites a pyrotechnic material adjacent the heater element which burns a propellant. Thisproduces gas to inflate the airbag.A particular concern to automotive manufacturers is the possibility of igniter devices firing inadvertently due to a fault. For example, inadvertent firing of an airbag igniter device could have serious consequences for a driver whilst driving. Two of the major type of faults which can occur in igniter devices are: 1) improper connections to either side of the igniter element; and 2) faulty igniter elements themselves. It is therefore common to have both high and low side switches coupled tothe igniter element by wires to ensure that a fault, such as improper connection to the igniter element, does not fire the igniter device.However, the igniter device may still be inadvertently fired due to Electrical Static Discharge (ESD) and/or RF energy induced in the long wires between the high and low side switches and the igniter element. This problem can be mitigated byusing a hot wire bridge igniter element which has a low resistance of 2 ohms and 1.5 Amps (A) for 3 ms firing conditions. That is, 13 milli-Joules (mJ) of energy is required to fire the hot wire bridge. The required firing energy is thus relativelyhigh compared to the typical ESD and RF induced energies and thus this solution provides some protection against induced currents. However, in view of the increase in RF sour

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